The current ultrastructural study of cultured explants of bovine and rabbit posterior ciliary processes using immunoglobulin (Ig) G-opsonized red blood cells (E-IgG) showed specific IgG Fc receptor-mediated attachment, ingestion, and digestion of IgG-coated erythrocytes by the pigmented epithelium (PE). Nonpigmented epithelial cells (NPE) in the cultured explants and a transformed cell line of bovine NPE, with and without lymphokine stimulation, did not have IgG-receptor activity. The interaction between PE and E-IgG involved the extension of micropseudopods toward adherent E-IgG, the formation of a linear uniform cap of roughly 200 A between opposing cell membranes, the ingestion of E-IgG by PE into a membrane-lined compartment, and the disintegration of the ingested ligand into membranous debris. Disintegration of some surface-associated E-IgG was also observed and was consistent with the release of a lytic substance by the receptor-activated PE.